Quantum information is information that is held in the "state" of a quantum system. The most popular unit of quantum information is the qubit, a two-state quantum system. However, unlike classical digital states (which are discrete), a two-state quantum system can actually be in a superposition of the two states at any given time. So in reality, the quantum system has an infinite number of possible states.
Quantum information differs from classical information in several respects, among which we note the following:
- it cannot generally be read or duplicated without disturbance (no cloning theorem)
- it can exist in superpositions of different values; quantum information is exponentially more efficient than classical one, as one state can exist in superposition of all possible states at once.
- quantum information is probabilistic in nature.
Shannon entropy
The Shannon entropy of a quantum ensemble with the density matrix ρ is given by -Tr[ρln(ρ)].
D-Wave Systems - D-Wave is "the" quantum computing company. Based out of Vancouver, British Columbia, they are currently the only company in the world pursuing the development of quantum computing hardware and software.External links: